Insulation of metal bodies



July 12A, 1932. H. LATHRoP INSULATION OF METAL BDIES Filed Nov. 2l, 1930 m.\\. .llllllllnlll Ill! /N VEN TOR H. LA THROP Arron/mf Patented July 12, 1932 uNl'rEDj srafras PATanli orf-Alca man LAfrrmor, or eannnwrcn, ooNNnmcU'nAssIcNoa To BELL TELEPHONE' LAnoaAronIns, mconronArnn, or Naw Yoan, 'nt-Y., 'A coaroaArronf or Naw v YORK msunArIoN or imrAL nomas Application illedrl'ovembcr 21, 1980. Serial'l'o. 497,261.

This invention relates to electrical insulation, and particularly to the insulation of metals iniinely divided form; such as the magnetic ribbpnsor sheets used inthe manufacture of magnetic elements for inductance devices.

An object 'of the invention is to applya permanent electrical insulation on metal material of the above-mentioned kind, which m Vwill not deteriorate when subjected Subsc-- quently to mechanical forming processes and to heat treatments at high temperatures.

The invention has specic application to inductance devices of the type employing mag- 15 netic elements composed of very thin ribbons or sheets of magnetic material insulated @from each other b electrically insulating material to reduce e dy current losses, such as transformers, and' so-called magnetic crossgg talk -ad'ustinlg coils or beads. In the case especia y, w ere the magnetic elements of such -devices are made from magnetic alloys f containin nickel and iron, it is often desirableto su ject them to a subsequent annealing heat treatment at a very high temperature to improve their magnetic properties ".fand to remove 'the strains produced therein bypreceding mechanical forming processes tending to impair the desirable electrical an 'n30 magnetic properties of the magnetic alloy,

which are otherwise obtainable. v

In general, an .insulating material .to be suitablefor insulating finely divided metallic material, for example, the magnetic elements used in magnetic bodies, requiring subsequent mechanical and thermal treatments, must be one 'which will have suiiicient strength to withstand the mechanical treatment, a high resistance to decomposition by heat, and

'40 one which will satisfactorily adhere tol the permanent insulation thereon.

- In accordance with the inventionit'has been found that. an insulation having the above-mentioned advantageous properties metallic material so as lto, give a uniform,

.talk therein, so-called ma justing beads, one of whlchisillustrated 1n 90 may be Aobtained on metallic elements, for example, .on the thin sheets or ribbons of magnetlc materialy used in inductance devices, by applying thereto a suspension of finely divided insulating material such as colloidal clay (kaolin), talc, or other nely divided materlal of similar characteristics, in a suitable organic liquid suspending medium which will evaporate at ordinary room temperatures, such as acetone or ethylene dichloride. When the metallic material is in the form of a thin ribbon, sheet or tape, the insulating material may be applied thereto by momentarily immersing in, or drawing the ribbon, sheet or tape, quickly throu h the suspension of insulating material w e rapidly stirring the latter. If the thin metallic material is wound or formed 'into its final form before the organic medium has c cmpletelyr evaporated, a ermanent adherent electrical insulation wi be'produced on the surfaces ot the formed metallic material, which will not deteriorate when subjected to a subsequent heat treatment at extremely high temperatures. The details of the invention and the ad-4 vantages thereof will be clearI from ,the fcllowing detailed description lthereof'when read 1n connection wit the accompanying drawing: v o

Figs. 1 and 2 of which show magnified views of portions of a magnetic cross-talk adjusting coil or bead to which the process of the invention is particularly applicable; and

Fig. shows diagrammatically one way of making the roduct illustrated in Fi r. 1 and 2 utilizingt e insulating process o the invention.

The inventionwill be described as a plied to the insulation of small magnetic co s utilized for correcting for the mductance un- 'balances in the line windings Vof loading units inv telephone circuits so as to minimize crossetic cross-talk ad- Fig. l, but it is applicable as Well'to the insulation of magnetic materials for use in other types of magnetic bodies and to the insulation of metallic materials in general which must be subjected subsequently to mechanical forming `processes and to heat treatments at very high temperatures.,v

Fig. 1 shows in magnifiedform a plan View of a magnetic cross-talk adjusting bead or coil of the type to which the process ci the invention is particularly applicable, and Fig. 2 shows an enlarged cross section of a eW turns thereof taken along the line A. As indicated in Figs. l and 2, the bead comprises a closely Wound spiral of thin, dat ribbon of a magnetic metal, such as a magnetic alloy including nickel and iron, and adherent iusulating material between the adjacent turns of the spiral. In a commercial product utilized for adjusting the inductance of telephone loading coils, the bead comprises approximately 40 turns of a magnetic ribbon coated with insulating material, about l@ inch Wide by 0.003 inch thick, the outside diameter of this spiral being approximately 1{2 inch, and the inside diameter approximate y 0.06 inch to 0.08 inch. The material of the magnetic ribbon in said commercial product comprises a magnetic alloy including nickel, iron and molybdenum. The outer end of spiral is secured by spot Welding to the preceding turn. j l

To properly develop the magnetic properties of the magnetic material in such a bead,

it is desirable to subject it after the insulating and forming process to an annealing heat treatment at a very high temperature of the order of 500 C. or more, the particular heat treatment used depending upon the constituents ofthe magnetic material and the breakdown temperature of the insulating material to remove the strains therein which tend to impair the magnetic properties of the ma netic material which otherwise would be o tained. This is usually accomplished by heating the bead or beads placed in a sealed pot in a suitable furnace at the desired temperature for about an hour, and then allowing it to cool in the furnace. The insulation bet-Ween the adjacent turns of the' magnetic ribbon in the spiral, therefore, should be such as will withstand Without deterioration from a mechanical and electrical standpoint,

'a suspension 4: of colloidal clay in an organic suspending liquid which will volatilize quickly at roo-m temperatures, such as acetone or ethylene dichloride, in a suitable container 5, While the suspension is continuously stirred. Then the magnetic ribbon so treated is exposed to the atmosphere, which may be air or other gas at ordinary room temperatures, the acetone or ethylenedichloride evaporates leaving an adherent insulating coating of the colloidal clay (kaolin) on the surfaces of the ribbon. rlhe magnetic ribbon so treated is preferably formed by suitable mechanical means into its final form, in this case a closely Wound spiral of the magnetic ribbon with the insulation between adjacent turns, for example, as illustrated in Fig. 3, by Winding it on the drum 6 rotated at the proper speed by means of the belt 7, during the period 'while acetone or ethylene dichloride is evaporating. The coating of colloidal clay on the surfaces of the magnetic ribbon forms a permanent insulation between the turns of the spiral in the cross-talk adjusting bead. It has been found that when the suspension used comprises approximately one `part of colloidal clay to six parts of acetone, by Weight, the insulating coating is suiciently adherent to the magnetic material to Withstand without deterioration from a mechanical standpoint the forming operation and the usual mechanical handling to which cross-talk adjusting beads aresubjected in service, and to lwithstand without deterioration from an electrical insulating standpoint a subsequent annealing heat treatment at a temperature in the order of 1,000 C. or more to remove strains and to improve the magnet-ic characteristics of the magnetic material in the bead.

' Other insulating materials besides colloida claysv may be used if they are such as will withstand the' high temperatures of thel annealing heat treatment to which the magnetic material is to be subjected. For example, approximately the same proportions of colloidal talc has been vfound to be a suitablesubstitute for the colloidal clay.

One of the important applications of the invention is in connection with magnetic cores for transformers and the like Where the core comprises thin sheets or layers of a magnetic material separated by insulating material, especially Where the magnetic material in the core is such as to require a subsequent annealing heat treatment at a very high temperature to properly develop the magnetic characteristics 'of the magnetic materialf A lt is to be understood that the invention is not limited to the particular magnetic mai illustrated and described Jor carrying out the process of the invention, which have been given by Way of example only, and that any other suitable magnetic and insulating materials, proportions of the materials in the suspension, and mechanisms may be used within the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. The process of applying a permanent, adherent coating of an insulating material to a metal body requiring subsequent heat treatment at high temperatures, which -consists in mixing the insulating material in colloidal form with an organic liquid comrising acetone to form a suspension of said insulating material, immersing said body in said suspension while rapidly stirring the latter to coat said body, and then exposing the coated body to the atmosphere to evaporate the acetone. J

. 2. The process of making a magnetic body from sheet magnetic material and insulating material, which consists in making a suspension of the insulating material in finely divided form, in an organicliquid suspending medium having the property of evaporating quickly in air ,at ordinary room temperatures, drawing the magnetic sheets through the suspension while rapidly stirring the lat-l ter to coat the sheets with the organic liquid and insulation mixture, and thenexposing the coated sheets to the atmosphere while forming the magnetic body therefrom, to vaporize xthe organic liquid and produce aderent, solid coatings of the insulating material on the magnetic sheets. y 3.. The process of making a magnetic body comprising adherent, alternate layers of sheet magnetic material and clay insulating material, which suspension of the clay in a suspending me- 'dium comprising acetone in the approximate proportions by weight of one part clay to six parts acetone, immersing te magnetic sheets in said suspenion while rapidly stir ring the latter to form liquid coatings thereof on said sheet, and then exposing the coated sheets to the atmospherewhile forming them into a compact mass in the desired form, to vaporize the acetone and produce adherent, solid coatings of clay on, the magnetic sheets.

4. The process of making a magnetic body comprising adherent, alternate layers of sheet magnetic material and talcinsulating material, which consists in making a colloidal suspension of the talc in a suspending medium comprising ethylenev dichloride in the approximate proportions by weight of one part talc to six parts ethylene dichloride, immercing sion while rapidlvstirring the latter to form liquid coatings thereof on said sheets, and then exposing the coated sheets to air while simultaneously formin them into a compact mass in the desired orm, to vaporize the ethylene dichloride and produce solid, adherent coatings of talc on said sheets.l

consists in making a colloidal the magnetic sheets invsaid suspen- 5. Ali insulating composition comprising a suspension of finely divided insulating material in acetone.

6. The composition of claim 5 and in which siid insulating material comprises colloidal c ay.

7 The composition of claim 5 and in which sad insulating material comprises colloidal ta c. i Y

In witness whereof, I hereunto subscrih my name this 11th day of November 1930.

HUBBEL LATHRoP. 

